I've been noticing this in other saves, every time I play on Sunset Valley there's some resident (like the premades) female sims wearing the clothes (and even hair) that came with Supernatural, but the weird thing is that they're not random, even the colors are matching, and those styles weren't saved on CAS to be randomly chosen by the game! Once I opened a sim wearing like this on CAS via Master Controller and it was the only outfit showing up, and named as "Special".

What is this? I'm curious...

Here's an example of what I'm talking about:

These are the outfits they get from the magic mirror whenever they choose "Magical Makeover". This interaction is set to be autonomous and Sims are quite addicted to it.
To prevent this in the future either delete all magic mirrors in your game or use a mod to make the interaction non-autonomous. I think there's one at simsasylum.com.

I'm going to scatter magic mirrors in my worlds cuz my sims have less fashion sense than I do.

I have noticed that the outfits given by the game in CAS and to inactives and service sims also look non-random a lot of the time (all the time in my game): color-coordinated, oddly logical. Only the accessories look truly random.

Silly me for not noticing that it was because of the magic mirror
And in my game 95% of the random outfits are the weirdest combination possible, even makes those from the magic mirror better :P

Most people who talk about game outfit assignment report experiences nearer to yours than mine. Sometimes I feel disappointed that I don't get to witness more of it. Though that hideous hockey mask showed up a couple times.

Yeah, I should have edited your screenshot and add a huge arrow pointing to the mirror and write: There's your culprit!